Injection blow molding is a two-stage process customarily used in the manufacture of plastic products having a hollow configuration. In the first stage of the process, plastic is injection molded, usually over a steel core rod or pin, into a preform cavity where a partially shaped mass of plastic is pre-formed into what is customarily called a parison, and this parison is temperature conditioned. In the second stage the parison is transferred while on the core rod into a blow mold, where air is introduced through the core rod and the parison is blown outwardly against the confines of the blow mold to its final shape, and cooled. The blown plastic product is then stripped off of the core rod and ejected from the machine.
In a typical injection blow molding machine a rotary turret is provided that has three or more surfaces. Each surface supports one or more core rod assemblies at each molding station. When the turret is rotated, the array of core rod assemblies are transferred successively between molds, i.e. moved sequentially from station to station. The first station is the parison station, which has an array of parison or preform molds, at which the parisons are injection molded on the core rod assemblies. Then the core rod assemblies carrying the parisons are rotated to another station having an array of blow molds, where the parisons are blown to form hollow articles, such as containers. Finally, the turret is rotated to bring the hollow articles to a point where they are removed from the core rods, thus permitting a new cycle to begin.
These core rod assemblies include a hollow core rod which provides a passageway for introducing the blowing medium, usually compressed air, into the parison to be inflated once inside the blow mold. The core rod's air passage is normally opened and closed by means of a spring-loaded core rod valve which admits air during the blow molding step. Opening of the valve is actuated by a push bar located within the rotating turret or transfer head. The push bar is activated either by a direct mechanical means or by pneumatic pistons acting on the push bar. The movement of the push bar is typically fixed and not adjustable, and always terminates against the end of the core rod which faces the push bar. The push bar applies force against the end of the core rod valve assembly when it contacts it in order to overcome the resistance of the spring to open the valve.
The valve opening or "stroke" determines the air flow into the unblown parison as well as determining the ease of venting of the compressed air from the blown hollow article prior to removing it from the blow mold. Since differing valve strokes will result in different amounts of parison movement in the blow mold and air flow into and out of the blown article, valve stroke is extremely critical to repeatability of the blow molding process from cavity to cavity and from cycle to cycle.
Consequently, these core rod valves must all be adjusted so as to stay open for a time sufficient to allow for a predetermined amount of air to be emitted which is necessary to produce the desired molded article. The core rod valve assembly comprises a valve stem located within the core rod and a valve element carried by the valve stem. The valve is urged into seating engagement with a valve seat by means of a core rod spring, whose sole function is to close the valve. The compressive force applied by the spring causes it to act to close the valve. The valve spring is held in place by a locking or "star" nut and a crowned hex or "cam" nut, both of which are threaded onto the valve stem and are located inside the core rod. The cam nut extends beyond the core rod housing. Actuation of the valve is caused by the pressure of the push bar on the cam nut. The amount of cam nut extension beyond the core rod housing determines the amount of valve stroke.
Adjustment of the stroke of the core rod valves has heretofore been accomplished by a multi-stepped process, employing a plurality of tools, jigs or fixtures. Typically, a hand tool may be employed, which basically comprises a pair of wrenches which are used to adjust the valve spring compression. Typically, one of the wrenches operates on the lock or star nut and the other operates on the hex or cam adjustment nut. Sequentially, the star nut is manipulated first to release its lock on the cam adjustment nut, and then the hex nut is adjusted to set the distance of the valve stroke by adjusting the amount of cam nut extension beyond the core rod housing. The tool is removed and the cam nut extension or valve stroke measurement is accomplished by means of a dial indicator, a "go-no go" mechanical positioning device, an electrical means employing limit switches and lights, or other measurement devices. The simplest approach is to employ a dial indicator to measure the adjusted position of the cam nut, or its setting relative to the core rod housing. Following this, the wrench is again employed to either readjust the cam nut, or if it has been adjusted to its desired position to achieve the desired stroke, then the wrench is used to manipulate the star nut to lock the cam nut in the adjusted position. Should the desired position of the hex nut not be attainable by the first effort, then the foregoing process is repeated until the desired adjusted position is attained. Each time a setting is made the wrench is moved into position and removed, followed by positioning of a dial indicator, or other measuring device, against the core rod assembly to take a reading so as to measure the adjustment, and thereafter re-applying and again manipulating the wrench, etc.
It is therefore desirable to provide a unitary tool for setting or adjusting, and simultaneously measuring the adjustment of, core rod valve lock nuts, cam nuts and stroke.
It is a further object of the invention to provide a unitary tool for core rods to adjust the stroke of the core rod valve so as to achieve a desired valve stroke, without having to repeatedly use and withdraw wrenches from the core rod assembly.
A still further object of the invention is to provide a tool for adjusting the valve stroke of core rods used in injection blow molding machines, which employs a pair of hollow wrenches which rotate to provide the adjustment and do not require translation of the wrenches.
Still another object of the invention is to provide a tool for adjusting the valve stroke of core rods used in injection blow molding machines which permits direct measurement of the valve stroke as the tool is in the process of making adjustment of the hex and star nuts of the core rod assembly.